There is a high expectation that devices using semiconductors such as GaN or InP are operable with high voltage at high speed. Utilizing the characteristics of these materials, an effort has been made to develop high-power amplifiers operating at high frequency, giving rise to expectations for highly efficient, high-power, broad-range amplifiers.
Circuit types of broad bandwidth amplifiers include distributed amplifiers. A distributed amplifier has a plurality of transistors arranged in a line, with the gate electrodes thereof being connected to each other through a wire, and the drain electrodes thereof being also connected to each other through a wire. The wire connecting the gate electrodes together serves as an input line, and the wire connecting the drain electrodes together serves as an output line. The wires are designed to have proper lengths determined based on the parasitic capacitances and the like of the transistors as well as to have proper impedances responsive to the wire widths and a substrate thickness, thereby providing an amplifier having a desired bandwidth. However, a distributed amplifier inevitably has the bandwidth thereof limited on higher frequencies due to the parasitic capacitances of the transistors and the shapes of wires between the transistors.